Field observations of gravel-bed river morphodynamics: perspectives and critical issues for testing of models

The discussion deals with field observations of river morphodynamics. In the first section it is discussed how new remote sensing techniques are making more feasible to carry out field studies in comparison with some years ago. The following section deals with channel stability. Identification of stability conditions (i.e. equilibrium or disequilibrium) is crucial to compare field observations and models appropriately, specifically for those models that assume equilibrium conditions. The last section concerns measurement of active channel width which has been recognized recently as a crucial parameter for improving the performance of analytical models and for understanding morphodynamics and sediment transport in braided rivers.